Single crystal silicon is the starting material in many processes for fabricating semiconductor electronic components and solar materials. For example, semiconductor wafers produced from silicon ingots are commonly used in the production of integrated circuit chips on which circuitry is printed. In the solar industry, single crystal silicon may be used instead of multicrystalline silicon due to the absence of grain boundaries and dislocations.
To produce the semiconductor or solar wafers, a single crystal silicon ingot may be produced by melting polycrystalline silicon in a crucible and solidifying it again for a direction solidification process, or dipping a seed crystal into the molten silicon, withdrawing the seed crystal in a manner sufficient to achieve the diameter desired for the ingot, and growing the ingot at that diameter for Czochralski process. For a continuous single crystal silicon process, the method is similar to that of a batch process except the polysilicon is fed and melted simultaneously with crystal growth. The silicon ingot is then machined into a desired shape from which the semiconductor or solar wafers can be produced.
During the process, oxygen is introduced into silicon crystal ingots through a melt-solid or melt crystal interface. The oxygen may cause various defects in wafers produced from the ingots, reducing the yield of semiconductor devices fabricated using the ingots. For example, insulated-gate bipolar transistors (IGBTs), high quality radio-frequency (RF), high resistivity silicon on insulator (HR-SOI), and charge trap layer SOI (CTL-SOI) applications typically require a low oxygen concentration in order to achieve high resistivity and to avoid formation of P-N junctions.
Due to the relatively low Oi, such wafers may have relatively weak mechanical strength and relatively poor slip performance at high temperature anneal/ramp that may be requested by a device manufacturer. The mechanical strength and slip performance of low Oi wafers may be improved by co-doping them with nitrogen or carbon.
At least some known methods use float zone materials to achieve a low oxygen concentration and high resistivity. However, float zone materials are relatively expensive and are limited to use in producing ingots having a diameter less than about 200 mm. Accordingly, these known methods are unable to produce higher diameter silicon crystal ingots with a relatively low oxygen concentration.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.